(1) Field of the Invention
The invention relates to a test system for digital miniature camera modules, and more particularly, to a system to test camera modules, to be used as built-in modules in consumer electronics as e.g. mobile phones or PDAs, performing electrical tests, adjustment of the focus, and sealing the lens barrel with glue.
(2) Description of the Prior Art
Camera modules intended to be used as built-in modules in hand-held consumer electronic devices as, e.g. mobile phones or PDAs, have to be fast and simple to be produced. Therefore said camera modules have usually a fixed-focus lens producing sharp images of objects located within a specified distance range. A typical requirement for a mobile phone camera is good focus between 0.4 m and infinity.
When such a camera is focused, perfect focus is only achieved for objects at a certain distance from the camera. Objects located at all other distances will be out of perfect focus, but may be still in acceptable focus. The term depth-of-field refers to a range over which the object can be moved and still be imaged with a blur not exceeding the acceptable one. For a fixed-focus camera having the requirement of a focus up to infinity the needed focus distance is called hyper-focal distance.
There are solutions published dealing with the testing of cameras:
U.S. Pat. No. 6,512,587 (to Marcus et al.) describes a method for determining whether an imager assembly outside of a camera body meets predetermined focus specifications, wherein the imager assembly includes an image sensor and a camera mounting plate having reference features adapted to cooperate with alignment features in the camera body to locate the image sensor at a predetermined focal plane, including the steps of: mounting the imager assembly onto an imager mounting apparatus having equivalent alignment features; and utilizing low-coherence light interferometry to determine whether the image sensor will meet predetermined focus specifications when mounted in a camera body.
U.S. Pat. No. 6,075,601 (to Marcus et al.) discloses an apparatus and method for calibrating an optical probe assembly, wherein the optical probe assembly includes a probe mounting surface and an optically transparent material spaced from the probe-mounting surface. The method includes providing a calibration apparatus, wherein the calibration apparatus includes a calibration mount having an axis and a reference surface on an exterior surface of the calibration mount. A calibration target is mounted substantially perpendicular to the calibration mount axis at a predetermined distance from the calibration mount reference surface, and a distance LR from the calibration target to the calibration mount reference surface is determined. The optical probe assembly is then removably mounted and lockably secured to the calibration apparatus such that the calibration mount reference surface is in a predetermined orientation relative to the probe-mounting surface on the optical probe assembly. Non-coherent light interferometry is used to determine a distance PR from the optically transparent material to the calibration target, and a distance LP from the probe-mounting surface to the optically transparent material using the values of LR and PR is determined.